Tailored recombinant elastin-like polymers for advanced biomedical and nano(bio)technological applications

The genetic engineering of protein-based polymers is a method that enables, in an easy way, the design of complex and highly functional macromolecules. As examples of this approach, different molecular designs are presented, with increasing degree of complexity, showing how the controlled increase in their complexity yields (multi)functional materials with more selected and sophisticated properties. The simplest designs show interesting properties already, but the adequate introduction of given chemical functions along the polymer chain provides an opportunity to expand the range of properties to enhanced smart behavior and self-assembly. Finally, examples are given where those molecular designs further incorporate selected bioactivities in order to develop materials for the most cutting edge applications in biomedicine and nano(bio)technology.     

Chiroptical and photochromic properties of stereoregular copolymers of 4-methacryloxyethylenoxyazobenzene with (−)-menthyl methacrylate

Copolymers of the photochromic monomer 4-methacryloxyethylenoxyazobenzene with the optically active comonomer (-)-menthyl methacrylate, having different stereoregularity, were investigated in order to obtain a better understanding of the relationship between microstructure and photochromism in synthetic macromolecules. No appreciable effect was observed by copolymer composition, sequence distribution, and microtacticity on the photoinduced trans → cis isomerization of the azobenzene side chains. This last, however, is reflected in changes of the chiroptical properties, type and entity of the photoinduced variation being dependent on chain structure. The long spacer separating the azo chromophore from the main chain limits the extent of chiroptical properties dependence on irradiation.     

Gene conversion vs point mutation in generating variability at the antigen recognition site of major histocompatibility complex loci

We have prepared a [³²p]-labeled oligonucleotide probe carrying a ureido (-NH-CO-NH₂) function at its 3-terminus. This labeled oligomer was used to study polycondensations of urea and formaldehyde and of various phenols and formaldehyde in aqueous solution. The formation of formaldehyde copolymers attached to the amido-function of the probe was monitored by gel electrophoresis. Our results are generally in agreement with those obtained using conventional techniques. Our method is suitable for monitoring potentially prebiotic polycondensation reactions involving formaldehyde.Abbreviations HBA 4-hydroxybenzoic acid, Na⁺ salt - HBzOH 2-hydroxybenzyl alcohol - HBSA 4-hydroxybenzenesulfonic acid, Na⁺ salt Correspondence to: L.E. Orgel     

Zinc complexes with tricarballylic acid and Lewis bases with zero- and two-dimensional structures

Three ternary zinc complexes of the open chain polycarboxylic acid, tricarballylic (1,2,3-propane-tricarboxylic) acid (PTCH₃) have been isolated and characterized with crystallographic and physicochemical techniques. [Zn(PTCH)(phen)(H₂O)]₂ · 4H₂O (1) (where phen = 1,10-phenanthroline) has a unique dinuclear structure, while [Zn(PTCH)(bpy)]_n · 3nH₂O (2) and [Zn(PTCH)(epy)]_n · 4nH₂O (3) (where bpy = 4,4′-bipyridine and epy = 1,2-bis(4-pyridine)ethane) have 2D polymeric structures. The bis-deprotonated ligand, in all three complexes, uses for coordination only two oxygen atoms, which belong to the same carboxylate in 1, and to two different carboxylates in 2 and 3.     

Molecularly imprinted polymers for the determination of a pharmaceutical development compound in plasma using 96-well MISPE technology

The use of molecularly imprinted polymers (MIPs) as sorbents for the solid phase extraction (SPE) of a pharmaceutical compound in development, prior to quantitative analysis was investigated. Three MIPs were synthesised using a structural analogue as the template molecule. Each polymer was prepared with different monomers and porogens. The MIPs were then tested for their performance both in organic and aqueous environments, the final aim being to load plasma directly onto the polymers. At an early development stage, there is a limited amount of compound available. Due to this limitation, reducing the amount of template required for imprinting was investigated. A MIP capable of extracting the analyte directly from plasma was produced. The specificity of the polymer allowed the method to be validated at a lower sensitivity than a more conventional SPE assay. For the first time, MIPs were packed into 96-well blocks enabling high throughput analysis. The analytical method was fully validated for imprecision and inaccuracy down to 4 ng/ml in plasma.     

Partitioning of peptides and recombinant protein–peptide fusions in thermoseparating aqueous two-phase systems: effect of peptide primary structure

Genetic engineering has been used for fusion of peptides, with different length and composition, on a protein to study the effect on partitioning in an aqueous two-phase system. The system was composed of dextran and the thermoseparating ethylene oxide–propylene oxide random copolymer, EO30PO70. Peptides containing tryptophan, proline, arginine or aspartate residues were fused at the C-terminus of the recombinant protein ZZ-cutinase. The aim was to find effective tags for the lipolytic enzyme cutinase for large-scale extraction. The target protein and peptide tags were partitioned separately and then together in the fusion proteins in order to gain increased understanding of the influence of certain amino acid residues on the partitioning. The salt K₂SO₄ was used to reduce the charge dependent salt effects on partitioning and to evaluate the contribution to the partition coefficient from the hydrophobic–hydrophilic properties of the amino acid residues. The effect of Trp on peptide partitioning was independent of the difference in primary structure for (Trp)n, (Trp-Pro)n, (Ala-Trp-Trp-Pro)n and was only determined by the number of Trp. The effect of the charged residues, Arg and Asp, was dependent on the surrounding residues, i.e. if they were situated next to Trp or not. The partitioning behaviour observed for the peptides was qualitatively and in some cases also quantitatively the same as for the fusion proteins. The effect of the salts sodium perchlorate and triethylammonium phosphate on the partitioning was also studied. The salt effects observed for the peptides were qualitatively similar to the effects observed for the fusion proteins.     

Electronic structure of siloxene model compounds

The electronic structures of one-dimensional and two-dimensional siloxene (Si₆O₃H₆) model compounds have been examined theoretically, using the semiempirical tight-binding self-consistent field crystal orbital (SCF-CO) method. These compounds are formed by silicon-based chain and planar structures containing a regular array of oxygen atoms. Results show that the two-dimensional polysilane in which OH groups are substituted for H atoms possesses a relatively smaller direct gap than other siloxenes. It is assumed that the electronic structures of siloxenes are affected not only by the dimensionality of Si-Si -conjugational networks due to an array of oxygen atoms, but also by the diminishing of the electron population in the Si-Si bonding orbitals caused by oxygen atoms with large electronegativity.     

Molecularly imprinted polymers in pseudoimmunoassay

Immunoassays are a class of analytical techniques based on the selective affinity of a biological antibody for its antigen. Competitive binding assays, of which the radioimmunoassay (RIA) was the first example, are based on the competition between analyte and a labelled probe for a limited number of binding sites. Molecularly imprinted polymers (MIPs) have been shown to be suitable replacements for biological antibodies in such techniques. Molecularly imprinted sorbent assays (MIAs) similar to RIA have been developed for a range of analytes of clinical and environmental interest. Limits of detection and selectivities of such assays are often similar to those using biological antibodies. Some assays have been used for measurements directly in biological fluids. The field is reviewed and it is shown that some perceived disadvantages of MIPs do not hinder their application in competitive binding assays: many MIAs have been demonstrated in aqueous solvents, and it has been shown that the quantity of template required to prepare imprinted polymers can be drastically reduced, and that binding site heterogeneity is not a problem as long as the sites which bind the probe most strongly are selective. Finally, recent developments including assays in microtitre plates, the use of enzyme-labelled probes, flow-injection assays and a scintillation proximity MIA are discussed.     

Molecularly imprinted polymer formats for capillary electrochromatography

The research aimed towards the adaptation of molecularly imprinted polymers (MIPs) to the capillary format and the use of these highly selective matrices for capillary electrochromatography (CEC) is reviewed in this article. The MIP is prepared by incorporation of a template molecule into a polymerization protocol. After polymerization and extraction of the template from the resulting polymer a highly selective material with recognition cavities complementary to the template in size, shape and chemical functionality is obtained. MIPs have been used as recognition elements in several different analytical techniques. In combination with CEC a novel separation system with a unique selectivity towards a predetermined target (the template) is achieved. The merge of molecular imprinting technology (MIT) and CEC have introduced several interesting polymer formats, due to the adaptation of the MIP to the miniaturized capillary format. The polymer formats can be classified according to their preparation protocols and appearance into three conceptually different categories, i.e. the monolith, the coating and the nanoparticles. The preparation protocols, characteristics and applications of these formats will be discussed.     

Self-association behaviour of atactic polymethacrylic acid in aqueous solution investigated by atomistic molecular dynamics simulations

The self-association behaviour of atactic poly(methacrylic acid) (a-PMA) in water was investigated by atomistic molecular dynamics (MD) simulations. Simulations show that interchain association of a-PMA occurs only in its un-neutralised form, by hydrogen bonding between –COOH groups, which is in agreement with the experimental observation. Chain conformations, dihedral angle distributions, hydration behaviour, scattering structure factor and enthalpy-of-hydration (i.e. aqueous solvation) were analysed as a function of concentration for un-neutralised PMA, across dilute to concentrated regimes. The average 〈R_g〉 of the chain remains unaffected in solution and also for amorphous undissolved a-PMA phase, confirming the occurrence of the approximate theta-solution condition for the first time, as revealed by simulations, in a polar hydrogen-bonding polymer aqueous solution. Chain hydration behaviour and scattering structure factor show significant changes in concentrated regime. Scattering intensity collapse occurs in concentrated PMA solution, due to the existence of the swollen regime captured for the first time by explicit-MD-simulations. The hydration of PMA is driven by H-bonding, specifically between H atoms of the COOH groups and O atoms of water molecules in the closest coordination shell. The enthalpy of hydration of PMA is dominated by PMA–water interactions (charges and H-bonding). The thermodynamic contributions of PMA–PMA and PMA–water interactions towards the electrostatics as well as the dispersion components of the total solvation-enthalpy become more favourable than water–water interactions.     

Molecularly imprinted polymers—A closer look at the control polymer used in determining the imprinting effect: A mini review

Molecular recognition displayed by naturally occurring receptors has continued to inspire new innovations aimed at developing systems that can mimic this natural phenomenon. Since 1930s, a technology called molecular imprinting for producing biomimetic receptors has been in place. In this technology, tailor made binding sites that selectively bind a given target analyte (also called template) are incorporated in a polymer matrix by polymerizing functional monomers and cross‐linking monomers around a target analyte followed by removal of the analyte to leave behind cavities specific to the analyte. The success of the imprinting process is defined by two main figures of merit, that is, the imprinting factor, and selectivity, which are determined by comparing the amount of target analyte or structural analogue bound by the molecularly imprinted polymer (MIP) and the nonimprinted polymer (NIP). NIP is a control synthesized alongside the MIP but in the absence of the template. However, questions arise on whether these figures of merit are reliable measures of the imprinting effect because of the significant differences between the MIP and the NIP in terms of their physical and chemical characteristics. Therefore, this review critically looks into this subject, with a view of defining the best approaches for determining the imprinting effect.     

The structure of polymer chains in confinement. A Monte Carlo study

A coarse-grained model of polymer star chains confined in two parallel impenetrable surfaces, which were attractive for polymer beads was studied. The flexible homopolymer chains were built of united atoms whose positions in space were restricted to vertices of a simple cubic lattice. The chains were modeled in good solvent conditions and, thus, there were no long-range specific interactions between polymer beads—only the excluded volume was present. The influence of the polymer density and the distances between the confining surfaces on the properties of star-branched polymers was studied. It is shown that the chains adsorbed on one surface could change their position so that they swap between both surfaces with frequency depending on the size of the slit and on the density of the system only. The increase of the polymer density diminished the frequency of jumps and caused that chains became only partially adsorbed. The analysis of structural elements of chains showed that the increase of the density of the system leads to increase of the number of bridges connecting the two adsorbing surfaces, thus, the frequency of jumps between them decreases.     

A growing family: New structures of coordination polymers containing adamantane-shaped phosphorus-nitrogen cage ligands

Two new structurally characterized coordination polymers containing the P₄(NR)₆ ligand system are described. A convenient one-pot synthesis of P₄(NR)₆ (R = benzyl) via reaction of lithiated primary amine with phosphorus trichloride demonstrates an expanded scope for the preparation of this adamantane-type structure. Reactions of P₄(NR)₆ (R = Et, Bn) with cuprous iodide yield different products due to the differences in steric demands of the ligands.     

海洋来源聚酚类化合物研究进展

近年来,从海洋动植物及微生物中分离出的许多结构新颖又有显著生理活性的天然聚酚类化合物,已经引起有机化学家和药学家的关注。我国海域辽阔,可开发利用的生物资源丰富,且开发利用的潜力巨大。2003年以来,我国该领域的不少科研成果在国际相关刊物上都有报道。本文对国内外海洋来源聚酚类化合物研究现状进行了综述,并按海洋聚酚来源的不同进行了分类,同时提出了海洋聚酚研究发展的趋势。     

Effect of polymers on enhanced chemiluminescent assays for peroxidase and peroxidase labels

Hydroxypropyl methylcellulose, hydroxyethyl cellulose, and hydroxybutyl methylcellulose stabilized light emission in a boronic acid-enhanced chemiluminescent assay for horseradish peroxidase. The stabilization of light emission was concentration-dependent and more effective with substituted boronic acid enhancers (e.g. 4-iodophenylboronic acid) than with substituted phenol enhancers (e.g. 4-iodophenol). Hydroxybutyl methylcellulose improved the linearity of the dose–response curve in a peroxidase-based antioxidant assay and stabilized light emission post-consumption of the antioxidant (Trolox). This polymer had no effect on the signal from a peroxidase label immobilized on a membrane (dot blot) or on the inside surface of a microwell in an enzyme immunoassay for thyrotropin.     

Porosity tuning of carborane-based metal-organic frameworks (MOFs) via coordination chemistry and ligand design

Two new metal-organic framework (MOF) materials based on boron-rich cluster struts (p-carborane) are reported herein. Cu(I) catalyzed coupling chemistry was used to synthesize carboxylate-based ligands, which are substantially longer than the previously studied dicarboxylated p-carborane, leading to structures with greater porosity. Solvothermal syntheses involving these ligands and Zn salts were used to prepare two new Zn(II)-based MOFs with 2D and 3D open framework structures. Upon thermal activation, these MOFs retain the chemical identity of their frameworks, leading to highly porous materials.     

Molecularly imprinted polymers for drug delivery

Molecular imprinting technology has an enormous potential for creating satisfactory drug dosage forms. Although its application in this field is just at an incipient stage, the use of MIPs in the design of new drug delivery systems (DDS) and devices useful in closely related fields, such as diagnostic sensors, is receiving increasing attention. Examples of MIP-based DDS can be found for the three main approaches developed to control the moment at which delivery should begin and/or the drug release rate, i.e. rate-programmed, activation-modulated, or feedback-regulated drug delivery. The utility of these systems for administering drugs by different routes (e.g. oral, ocular or transdermal) or trapping undesired substances under in vivo conditions is discussed. This review seeks to highlight the more remarkable advantages of the imprinting technique in the development of new efficient DDS as well as pointing out some possibilities to adapt the synthesis procedures to create systems compatible with both the relative instable drug molecules, especially of peptide nature, and the sensitive physiological tissues with which MIP-based DDS would enter into contact when administered. The prospects for future development are also analysed.     

Polymer-polymer organic solvent two-phase system: A new type of reaction medium for bioorganic synthesis

Mixing solutions of polymers dissolved in chloroform resulted in turbid solutions that parted into two separate phases upon standing. Each phase consisted primarily of one of the two polymers and contained only small amounts of the other. An enzyme (alpha-chymotrypsin) added to the two-phase system partitioned preferentially to one of the phases; this was observed with native enzyme and with enzyme associated with one of the polymers through non-convalent interactions. Under the conditions studied, alpha-chymotrypsin was active and expressed even higher activity and stability than native enzyme added to the organic solvent without polymer. An emulsion was easily formed on mixing with small droplets of one of the phases suspended in the other phase. By operating with the enzyme in the emulsion, a very attractive system for carrying out enzyme-catalyzed conversions was created. Short diffusion distances and minimized steric hindrance are two characteristics of such systems. At the conclusion of the reaction, stirring/mixing was ceased and, after phase separation, it was possible to recover the enzyme as well as the product, under ideal conditins, from different phases. The enzyme was then reused. (c) 1994 John Wiley & Sons, Inc.     

Characterization of molecularly imprinted polymers using a new polar solvent titration method

A new method of characterizing molecularly imprinted polymers (MIPs) was developed and tested, which provides a more accurate means of identifying and measuring the molecular imprinting effect. In the new polar solvent titration method, a series of imprinted and non‐imprinted polymers were prepared in solutions containing increasing concentrations of a polar solvent. The polar solvent additives systematically disrupted the templation and monomer aggregation processes in the prepolymerization solutions, and the extent of disruption was captured by the polymerization process. The changes in binding capacity within each series of polymers were measured, providing a quantitative assessment of the templation and monomer aggregation processes in the imprinted and non‐imprinted polymers. The new method was tested using three different diphenyl phosphate imprinted polymers made using three different urea functional monomers. Each monomer had varying efficiencies of templation and monomer aggregation. The new MIP characterization method was found to have several advantages. To independently verify the new characterization method, the MIPs were also characterized using traditional binding isotherm analyses. The two methods appeared to give consistent conclusions. First, the polar solvent titration method is less susceptible to false positives in identifying the imprinting effect. Second, the method is able to differentiate and quantify changes in binding capacity, as measured at a fixed guest and polymer concentration, arising from templation or monomer aggregation processes in the prepolymerization solution. Third, the method was also easy to carry out, taking advantage of the ease of preparing MIPs. Copyright © 2014 John Wiley & Sons, Ltd.